1. Field of the Invention
The present invention relates to a backlight driver of a liquid crystal display device, and more particularly, to a backlight driver of a liquid crystal display device and a method of driving the same, for simultaneously preventing backlight flicker and wavy noise by filtering an input synchronization signal.
2. Discussion of the Related Art
Representative examples of a flat display apparatus for displaying an image using digital data include a liquid crystal display (LCD) device using liquid crystal, a plasma display panel (PDP) using discharge of inert gas, a organic light emitting diode (OLED) display device using an OLED, and the like. Among these, the LCD device has been widely used in various application fields such as in a television (TV), a monitor, a notebook computer, and a portable phone.
An LCD device displays an image through a pixel matrix using the electrical and optical properties of liquid crystal having anisotropic properties with respect to refractive index, dielectric constant, and the like. Each pixel of the LCD device implements a gray level by adjusting optical transmittance with respect to a polarization plate using variation in liquid crystal arrangement direction according to a data signal. The LCD device includes a liquid crystal panel for displaying an image through the pixel matrix, a drive circuit for driving the liquid crystal panel, a backlight unit for irradiating light to the liquid crystal panel, and a backlight driver for driving the backlight unit.
The backlight driver for drive of the backlight unit controls the brightness of the backlight unit by adjusting on/off time of the backlight unit according to a duty ratio of a pulse width modulation (PWM) signal input from a TV set or a timing controller.
In this case, the backlight driver detects the duty ratio of the input PWM signal and reflects the detected duty ratio to a vertical synchronization signal input from a timing controller to generate and use an output PWM signal for control of the backlight unit in order to drive the backlight unit according to the liquid crystal panel.
The backlight driver receives a vertical synchronization signal (hereinafter, referred to as Vsync) for distinguishing a frame of image data from an external system or the timing controller and uses the Vsync in order to drive the backlight in synchronization with the liquid crystal panel.
However, in a conventional backlight driver, during a process in which a PWM drive frequency changes along with change in a frequency of an input image, that is, a frequency of an input Vsync, a PWM duty ratio is distorted to a recognizable level or more, resulting in backlight flicker, as shown in FIG. 1.
To address this problem, a method of preventing backlight flicker by slowly changing a PWM drive frequency when a frequency of the input Vsync changes has been suggested, as shown in FIG. 1B. However, when the PWM drive frequency is slowly changed, since synchronization with the input Vsync is distorted, wavy noise occurs.